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Thread: Guide scope for C-11 - ideas wanted

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    Default Guide scope for C-11 - ideas wanted



    I want to be able to use my C-11 for imaging small DSOs at its native 2800mm focal length. But after some major expenses, including notably a CEM60 mount to put the C-11 on, I don't really want to buy another scope as a gude scope. So I want to MacGyver a guide scope out of what I have, if I can.

    Option 1: Modify the C-11's finder
    I am not sure exactly what the finder is. It's Celestron orange, a right-angle illuminated-reticle finder. I'm guessing the focal length is around 200mm. I'm not sure this is enough to guide 2800mm. A 162mm finder-guider is good to 1700mm focal length, so 200mm should be good to 2100mm. Not enough, though maybe I could push it a bit. I'd probably have to have some kind of adapter fabricated.

    Option 2: Use my C-90 as-is
    It's an old model C-90, the f/11, 1000mm model. Kind of slow for guiding: I'm used to finding guide stars at f/3.3; not sure how it would work at f/11. But maybe it would work. I guess I should give it a try and see what it can see. I have the T adapter for this connection.

    Option 3: Use my C-90 with a reducer
    I have a .63 SCT focal reducer that would reduce the f/11 to f/7, if I can get it to fit. I believe, though I am not certain, that the old C-90 used the same threads as Meade ETX Maks. If so, I could use an ETX-SCT adapter, the 0.63 reducer, and then an SCT T-adapter to connect the camera. This would give me a guide scope focal length of 630mm at a focal ratio of f/7, considerably better. The cost of the adapters would be about $80.

    Option 4: Get a grip: do something normal

    I could always put the reducer on the C-11, bringing it down to 1764mm focal length, and then use my 162mm guide scope at its upper limit to guide it. But that would be too easy, and I want those little fuzzies to be big!

    I am open to evaluations, suggestions, etc.

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    DSO AP: Orion 200mm f/4 Newtonian Astrograph; ATIK 383L+; EFW2 filter wheel; Astrodon Ha,LRGB filters; KWIQ/QHY5 guide scope; Planetary AP: Celestron C-11; ZWO ASI120MC; Portable: Celestron C-8 on HEQ5 pro; C-90 on wedge; 20x80 binos; Etc: Canon 350D; Various EPs, etc. Obs: 8' Exploradome; iOptron CEM60 (pier);
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    Default Re: Guide scope for C-11 - ideas wanted

    Keith,

    My reply in two parts, first, what I am using, and second part, suggestions for your C90...

    I have a EdgeHD 11" on which I use a Orion ED80 APO, ($499) as the guidescope (as well as wide field imaging) which works very well without a focal reducer in either the guidescope or the OTA. My purpose is maximum reach for the distant fuzzies and planets. For this 80mm I use ADM mounting hardware, rings and ba to avoid flexure. I also use a Orion motorized focuser made for the EDE80 as all my system is operated via remote control. The mount is the Losmandy G11/Gemini II controlled via Ethernet...

    I have a second imaging setup, a ES127 ED/APO CF on which I have a Celestron 80mm guidescope mounted using the hardware it comes with on a ADM D bar piggybacked on the ES127 rings by removing the ES127 top handle and replacing it with the ADM D bar. I use a JMI focusing motor for remote control. This is on a CGEM-DX mount.

    As far as guidescope mounting hardware is concerned, I am a 100% believer in ADM hardware, which combined with the EdgeHD scope design mirror locks and a Moonlite draw tube focuser, flexure has not been an issue with the 2800mm OTA... And the ring set that comes with the Celestron 80mm guidescope are nearly identical to the ADM rings and very adequate in my opinion.


    As to the C90, I would suggest you run a test by temporarily mounting your guiding camera on the C90, and using the PHD viewing screen, see what stars can be seen with it.

    I have an older Celestron predecessor to the C5, it is a 750mm fl, however the mirror and focusing mechanism in it s too much motion (flexure) to be used for guiding. If you can solve that problem with your C90 (if it exists), I see no reason why it can not be used as a guidescope.

    Otherwise, I would suggest you consider the Celestron 80mm guidescope, I have been very happy with the one I have, the focuser is tight, I've not had any flexure issues with it. For $189, complete with ring set and camera mounting tube with M42 x 0.75 camera mounting thread included, I consider it to be the guidescope bargain of what is available...
    Thanks, Mitch - K1FH
    And sidekick Shadow, the precocious one
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    Default Re: Guide scope for C-11 - ideas wanted

    Thanks, Mitch. I'll keep the 80mm set in mind as a backup plan. At Cdn$279 with a dovetail mounting rail, it's a bit more than I want to spend at the moment. On the other hand, at f/7.5 / 600mm, it suggests that the C-90 with a reducer is a viable option at f/7, 630mm. And that option is only $80.

    Next step is to test the C-90 with my guide camera and see what it can see.

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    DSO AP: Orion 200mm f/4 Newtonian Astrograph; ATIK 383L+; EFW2 filter wheel; Astrodon Ha,LRGB filters; KWIQ/QHY5 guide scope; Planetary AP: Celestron C-11; ZWO ASI120MC; Portable: Celestron C-8 on HEQ5 pro; C-90 on wedge; 20x80 binos; Etc: Canon 350D; Various EPs, etc. Obs: 8' Exploradome; iOptron CEM60 (pier);
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    Default Re: Guide scope for C-11 - ideas wanted

    Quote Originally Posted by KeithBC View Post
    Thanks, Mitch. I'll keep the 80mm set in mind as a backup plan. At Cdn$279 with a dovetail mounting rail, it's a bit more than I want to spend at the moment. On the other hand, at f/7.5 / 600mm, it suggests that the C-90 with a reducer is a viable option at f/7, 630mm. And that option is only $80.

    Next step is to test the C-90 with my guide camera and see what it can see.
    Keith,

    I definitely would try the C90, especially as you have the camera adapter for it. I don't think the f11 will be an issue, I would expect any issue would be related to the mirror mount/focuser slop causing flexure...

    The price of $279cdn sounds unrealistic. When I read that, I went to Highpointscientific.com and checked the website to see what they are selling the Celestron 80mm guidescope package for, they have it listed at $159. If you ask, they will ship via USPS mail which might save you a bunch of money if my understanding (somewhat outdated) of how shipping products to Canada works.
    Thanks, Mitch - K1FH
    And sidekick Shadow, the precocious one
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    Default Re: Guide scope for C-11 - ideas wanted

    Quote Originally Posted by fmhill View Post
    The price of $279cdn sounds unrealistic. When I read that, I went to Highpointscientific.com and checked the website to see what they are selling the Celestron 80mm guidescope package for, they have it listed at $159. If you ask, they will ship via USPS mail which might save you a bunch of money if my understanding (somewhat outdated) of how shipping products to Canada works.
    Unfortunately, there is the exchange rate (currently, add about 15%) to consider. Shipping via USPS minimizes the shipping cost and avoids the couriers' brokerage fee scam at the border, but, for packages over $100, you get charged customs (add 10-15%). It quickly adds up to where buying from a Canadian retailer ends up being cheaper. The $279 price included the scope kit ($223) and the dovetail bar ($56) I would need to mount the rings on the C-11.
    Last edited by KathyNS; 12-30-2014 at 08:15 PM.

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    DSO AP: Orion 200mm f/4 Newtonian Astrograph; ATIK 383L+; EFW2 filter wheel; Astrodon Ha,LRGB filters; KWIQ/QHY5 guide scope; Planetary AP: Celestron C-11; ZWO ASI120MC; Portable: Celestron C-8 on HEQ5 pro; C-90 on wedge; 20x80 binos; Etc: Canon 350D; Various EPs, etc. Obs: 8' Exploradome; iOptron CEM60 (pier);
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    Default Re: Guide scope for C-11 - ideas wanted

    At 2800mm you are going to have a hard time getting great stars with a guide focal length below 1,000mm. Differential flexure is aSchmidt case grains biggest enemy and at 2800mm it will become quite noticeable. I would suggest a sensitive monochrome aptina sensor, qhy5L 2 or the asi120mm, I see that you already have the mc and that might be sensitive enough to do just fine, the qhy5 will have a hard time at f7. At 2,800mm you are going to be a lot better off with an off axis guider, like the orion TOAG. You have to get spacing and focus right but after that you can guide at the same focal length you image at which will give you nice stars. I think it can be taken a step further with meta guide which is designed to respond quicker to differential flexure through the use of an add on program called flexrx. I think the c90 could be another source of differential flexure depending on how much mirror flop it has but it's free because you have it so definitely give it a try. I think it might be a good way to test the guide abilities of the asi as well.
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    Default Re: Guide scope for C-11 - ideas wanted

    Quote Originally Posted by calypsob View Post
    I think the c90 could be another source of differential flexure depending on how much mirror flop it has
    One nice thing about the original C-90 is zero mirror flop. The primary mirror is glued to the rear casing. Focusing is done with the secondary.
    calypsob likes this.

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    DSO AP: Orion 200mm f/4 Newtonian Astrograph; ATIK 383L+; EFW2 filter wheel; Astrodon Ha,LRGB filters; KWIQ/QHY5 guide scope; Planetary AP: Celestron C-11; ZWO ASI120MC; Portable: Celestron C-8 on HEQ5 pro; C-90 on wedge; 20x80 binos; Etc: Canon 350D; Various EPs, etc. Obs: 8' Exploradome; iOptron CEM60 (pier);
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    Default Re: Guide scope for C-11 - ideas wanted

    I second Calypsob's comment about the use of MetaGuide. I've since moved to MG over PHD and although I am not utilizing the Flexrx addon (yet) I've found MG to really improve my guiding on my EdgeHD-11 at the full 2800mm.

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